Huge Volcano Clusters Found on Venus : Astronomy: Data from Magellan space probe reveals differences and similarities between Earth and its ‘sister planet.’ Scientists hope to map molten mantle’s circulation.

Scientists analyzing radar images from the Magellan space probe have discovered an enormous cluster of volcanoes on Venus, leading them to conclude that Earth and its seething “sister planet” are very different on the surface but may be remarkably similar under the skin.

“For the first time, we can put some numbers on some important features on the surface of Venus--the number of volcanoes, for example,” said planetary scientist Steve Saunders of the Jet Propulsion Laboratory in Pasadena. “It tells me how heat comes out of the interior. . . . Next, we would like to know why.”

JPL is using Magellan to map the gravity fields surrounding Venus. In this way, Saunders said, scientists hope to chart the convection, or circulation, of Venus’ mantle, the nearly molten rock layer between core and crust.

The computer-processed radar images from Magellan used for this new overview of the second planet from the sun show that the Venusian crust is measurably distended in some areas, compressed in others and pockmarked by 1,662 large volcanoes--30 times the number seen on Earth.

Most of these volcanoes are concentrated in a region near the Venusian equator, not stretched along the edges of tectonic plates as they are on Earth. Indeed, the scientists said, Venus almost certainly does not have the same kind of fractured surface as Earth.

But the radar images indicate that the mantle of Venus circulates in much the same fashion as the analogous layer of nearly molten rock inside Earth. This circulation causes rifts and sometimes volcanoes over areas of “upwelling,” where a blob of super-hot rock rises like the goop in a Lava Lamp.

This comprehensive view of Venus and its volcanoes was presented by three Brown University researchers--Lawrence S. Crumpler, James W. Head and Jayne C. Aubele--in the current issue of the journal Science.

Added to earlier evidence that Venus once may have had enough water for shallow seas, this new information hints at just how deliciously close the planet may have come to emulating the life-nurturing features of Earth--which is similar in size, density and distance from the sun.

In addition to finding significant clustering of its large volcano population, Crumpler said, this overview of Venus showed clearly how large crustal fissures on Venus also appear in clumps.

These groups of cracks in the planet’s surface tend to occur near volcano clusters. Crumpler said this indicates a bulge in the crust, probably because of mantle upwelling. Elsewhere, he said, volcanoes are scarce and the surface is rippling, or bunching up, as if being pulled in from below. This may be where cooler mantle material is sinking, or “downwelling.”

“Certain areas are stretching out and certain areas are being compressed together,” he said by telephone from a U.S. Geological Survey facility in Flagstaff, Ariz., where he and other scientists are analyzing the latest data from Magellan.

Identifying areas of expansion and compression will help scientists focus their effort to measure the planet’s gravity field.

“We have a model now that we can test with the gravity experiment,” he said.